What is rainwater harvesting and how does it work?
Rainwater harvesting is the capture, storage and use of rainwater. Anybody can do it and it can be designed and customized to suit the needs of the user (potable water from rainwater for example).
There are several types of rainwater harvesting systems, the following three are the main ones:
In-situ rainwater harvesting refers to the capture of rainwater where it falls. This system is useful in agricultural production systems where micro-catchments are used. For example Zai Pits ( Wikipedia Zai-Pits).
Run-off catchment is another rainwater harvesting system. Rainwater running of surfaces is channeled through pipes or trenches and collected in storage structures like tanks, ponds, swales (Wikipedia Swale ) and dams, to be used at a later stage or for attenuation and/or infiltration.
Then there are roof catchment systems. These involve capturing rainwater from roof tops and storing it either above or below ground tanks made from plastic, concrete or metal.
Some facts:
- In New Zealand around 10% of the population depend on roof collected rainwater.
- ~ 18% of total water consumption is used for flushing the toilet (domestic).
- ~ 23% of total water consumption is used for the washing machine (domestic).
- ~ 41% ( probably more if you add garden irrigation and outdoor use) of total water consumption could be covered by rainwater
- ~ 27% of total water consumption is used for showering (domestic)
(Watercare)
- Average water consumption per person in New Zealand 227 liters / day (Learnz). Water consumption varies quite significantly between the regions (Queenstown Lakes District Council 416 liter/day)
Advantages of Rainwater Harvesting
1. Low-cost Maintenance
You really don’t need to invest much money to keep the systems going. Purifying the water is not necessary if you don’t intend to drink the water.
2. Lower Water Bills
You can use your collected rainwater for flushing toilets, washing your clothes, and watering the garden. This’ll help in keeping your water bills to a minimum. (Sample system)
3. Great for Irrigation
Rainwater is pure rainwater without any added chemicals into it so you can make sure that this is reliable for irrigation. (Sample System)
4. Reduces Ground Water Demand
As our population increases, so does the demand for water. In many areas, we are reliant on dams, rivers and aquifers for our water sources.
5. Reduces Soil Erosion and Floods
By collecting rainwater, you can minimize the likelihood of flooding around your home and reduce the load on the council stormwater system.
6. Multi-Purpose
You can use rainwater in flushing down toilets, washing your cars and motorcycles, and etc. (Sample System)
Disadvantages of Rainwater Harvesting
1. Unreliable Rainfall
Rain doesn’t fall every day making it hard for you to collect some daily. However, for example, Auckland and other part of the country does not suffer from this compared to other centers.
2. Starting Costs
If you choose to have a rain harvesting system, then the time to implement these systems is when you are building your home as the additional costs are recovered quicker. Allocating funds for a system installed in your home is money well spent and will add value to your home.
3. Chemical roof seepage
Some roof coatings may contain harmful chemicals so it is advisable to talk with one of our consultants first to ensure your roof meets the guidelines.
5. Storage limits
There is a practical limit to how much water you can store on your property and is often limited by your section size and appropriate locations for the tanks . Especially in winter, the rain captured will be greater than the capacity of the tank. Rainwater tanks have to be designed to deal with this situation and to release the excess water to the council stormwater system in accordance with council requirements.
Rainwater Harvesting is a win-win situation for building owners, councils and the environment.
We can give you advice what systems will suit your needs and what is involved.
www.aloaqua.co.nz / [email protected] / + 64 3 2600 589
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Christchurch water charges to be considered next year
Gardening is a major user of water, particularly in the Garden City.
Staff are working on a report on ways the city's water can be priced, which will likely include a volumetric charge. The issue will be included in next year's Long Term Plan (LTP) process.
Water currently comes under a general rates bill, meaning water costs are tied to a property's value. A volumetric rate would charge for the amount of water used, encouraging people to use less.
Espresso Carwash Cafe co-owner Damian Curtain was relaxed about the prospect of a volumetric water charge as his business was environmentally friendly and not a big water user.
READ MORE: Water charges on the horizon
Christchurch uses about 129 million litres of water per day, which nearly doubles over the summer months, primarily because of irrigation for gardening.
Usage per person is about double that of Auckland, which charges about $1.40 per 1000L.
The water charging review came up in a council subcommittee discussion this week about promoting the use of rainwater tanks.
The last time the prospect of a water charge came up was 2015, during the last LTP review. The idea was dropped.
"There is a piece of work going on for the LTP looking at the review of water pricing," said John Mackie, head of three waters and waste, when asked if it was back on the agenda.
Demand for water in Christchurch is expected to rise as the population grows. The climate of eastern Canterbury is expected to become more dry in the coming decades, adding further pressure.
Councillors at the meeting said there was a clear need to conserve more water and changing the pricing method could achieve that.
"My position isn't necessarily that we charge for water, but we'll need to come up with a position that makes the people of Christchurch respect what's in our taps a lot more than what we currently do," councillor Aaron Keown said.
"We [currently] charge based on the price of your property, so a little old lady in Fendalton is paying five times more for her water than a flat of young fellas in Linwood. There's no reason for her to save her rainwater... or the guys to save theirs."
He said a volumetric charge would have little impact on the average ratepayer.
"It would only be cents. But it's the fact that mentally you're thinking 'I'm saving money' ... you change behaviours."
Christchurch Beautifying Association president Ron Andrew said the group "would strenuously oppose" a volumetric water fee in the city.
"It's absolute nonsense to say water's not available," he said.
"We are the Garden City and, if we're going to be honest to ourselves when we talk about the Garden City, then we have to provide two things: maintenance and, of course, water."
Andrew said gardeners using excessive water every day was a "myth".
Others used "far more water than they have to" washing cars, houses and flushing toilets. He believed a volumetric fee system would negatively affect those who needed more water.
"People will stop using water and so the cost will go on fewer people. I would expect it [the cost] would then go up."
Damian Curtain, co-owner of Addington's Espresso Carwash Franchise Ltd, was not concerned as his business was environmentally friendly and not a large water user.
Cars were washed with a fine spray so each clean used about 30 litres of water, he said.
Most Christchurch houses already have water meters installed.
Saving water would have economic and environmental benefits. Extracting the groundwater and handling wastewater came at a cost.
Earlier this year, an OECD report into New Zealand's environmental performance recommended councils adopt volumetric charging for water.
It said water consumption per household in Auckland had fallen 30 per cent since a volumetric charge was introduced in the late 1990s.
There were similar reductions in Nelson and Tauranga, where volumetric charging was introduced.
It is illegal for councils to profit from water, so a volumetric rate would be based on the cost of supplying water.
Council city services manager David Adamson said on Friday staff were "looking at the existing infrastructure and what is feasible around volumetric charging".
Whether it was included in the LTP was a council decision.
A council staff report into subsidising rainwater tanks found there would be little benefit, primarily because there was no financial incentive to conserve water.
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Rainwater Infiltration - Complete solutions for trench and trough-trench infiltration
Trench System
Trench systems are ideal when the surface above the infiltration system shall be usable, parking, playground etc.
Trough-Trench System
The polluted rainwater is cleaned via bio-active soil and seeps into the underlying trench, where it is stored short term to infiltrate.
Rainwater Retention / Attenuation - to ease pressure on public drainage infrastructure
Trench System
Rainwater is filtered through a sedimentation/ filter shaft, then stored short-term in the in-ground trench and slowly released via the throttle outlet. The system can remain open at the sides and bottom if local infiltration is allowed or desired. The tunnel elements are placed in a layer of EPDM material if a closed system is required.
Under- or above ground Systems
Selection of interconnected tanks, scalable to meet council and local requirements.
